GMC Troubleshooting Questions? Ask a Mechanic for Answers
Hi Im Dave, lets try this first: You must relearn your actuator to blow hot or cold correctly. Turn on your A/C to the highest blower setting and let it run 5 minutes, then dial up the heat leaving the blower in highest position for five minutes. this should resent your actuator to correctly blow hot or cold. ..that's one way to fix it.
have you tried this procedure?